In recent years, advances in technology, as well as ever evolving tastes in style, have led to substantial changes in the techniques used to design and build automobiles. One of the changes involves the complexity of the various electrical systems within automobiles.
Modern automobiles often employ dozens of electrical systems for monitoring and controlling virtually every aspect of operation. One of the electrical systems that is becoming increasingly common in automobiles of all types is known as Electronic Stability Control (ESC). ESC systems improve the handling of automobiles by selectively adjusting the activity of wheels to reduce vehicle understeer and oversteer tendencies. ESC systems often utilize anti-lock braking systems (ABS) and traction control systems (TCS), which are designed to prevent the wheels from slipping, or “spinning,” by reducing the braking force and power to the wheels, respectively.
In order for ESC systems to operate effectively, an accurate estimation of the reference velocity (i.e., the speed of the automobile relative to the driving surface) is required, even during control actions such ESC, ABS, and/or TCS. In order to calculate speed, automobiles typically use wheel speed sensors, and in recent years, acceleration sensors (e.g., accelerometers) have also been utilized. Wheel speed sensors are known for being quite accurate. However, wheel speed sensors are used to calculate vehicle speed by simply detecting the rate of rotation of each wheel, without taking into effect the rotation of the wheel relative to the driving surface. As a result, wheel speed sensors may indicate a high vehicle speed and/or acceleration, when in fact the wheels are losing traction with the driving surface and thus spinning. Acceleration sensors, on the other hand, are considered to be reliable as they provide an absolute measure of the acceleration of the automobile regardless of the traction that the wheels have on the driving surface. However, acceleration sensors are known to provide “noisy” electrical signals and are often corrupted by gravitational forces, which adversely affect the accuracy of any speed calculation.
Accurately estimating reference velocity is particularly difficult in four-wheel drive (4WD) and all-wheel drive (AWD) vehicles because, for example, power is provided to all of the wheels on the vehicle. As a result, all of the wheel speed sensors on the vehicle may be inaccurately indicating the velocity of the vehicle, as when all of the wheels are spinning (or slipping) simultaneously.
Accordingly, it is desirable to provide a method and system for determining the velocity of a vehicle which selectively utilizes various types of sensors. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.